Hi
I am trying to implement the following acoustic communication
transmitter with PC
File Source --> Packet encoder --> gmsk mod --> Rational resampler
–> Frequency Xlating FIR filter --> comp to real --> audio sink
Pc has inbuilt sound card. packet encoder is taking 8 samples per
symbol, Resampler interpolates samples by 500, FIR filter is set at 19k
carrier frequency and 1K bandwidth.
The problem is that I wont get any sort of output at the audio sink. I
added an GUI FFT sink at the end of FIR filter, it also showed now
output. Please tell what’s gone wrong. I am using gnuradio 3.7.4
version.
Thanks in advance
Hello Sreena,
the frequency translating FIR translates and then filters, ie. it moves
your baseband signal to -19kHz and then filters a 1kHz band around 0Hz
– thus cutting away all your signal.
By the way: I assume you want to produce sounds at 19kHz with your
built-in sound card: you won’t hear much [1] unless you’re very young,
and your sound card has wide filters – most cost-conscious soundcards
will simply have only exactly one very simple analog filter with a
cutoff frequency around 20kHz, and don’t pay much attention to a narrow
transition width, since humans won’t easily notice attenuation in
frequencies they can barely perceive anymore, and most speakers won’t be
linear at high frequencies, either.
Greetings,
Marcus